Lightning Heats the Air to 53,000 Degrees F

A single bolt of lightning has 20 times the energy of a car roaring down a highway at 60 miles per hour. It can heat the air around the spot where it hits the ground to a mind-boggling 53,000 degrees F.

In a study, recently published in the Nature publication Scientific Reports, South Florida School of Geosciences Associate Professor Matthew Pasek and his colleague Marc Hurst of Independent Geological Sciences, Inc. describe a new method to determine the amount energy expended by a bolt of cloud-to-ground lightning.

Measuring the energy in lightning has been a longtime challenge for scientists. Atmospheric physicists, for example, have studied artificially-induced lightning, which they create by firing small rockets into thunderclouds, with wires attached that lead to strike rods on the ground. Instruments on the ground have measured the temperature and electrical current from the artificial bolts, providing data used to calculate the approximate amount of energy in them.

But Pasek and Hurst have come up with a way to use geology instead. In the study, they examined 250 samples of fulgurites --pieces of glass formed when lightning strikes quartz sand or rock in the ground -- from mines in Polk County, Fla. In particular, they focused on the length and circumference of the fulgurite cylinders, whose dimensions enabled them to calculate more precisely the amount of energy released into the ground.

"Everyone knows there is a lot of energy in a lightning bolt, but how much?" Pasek explained in a press release. "Ours is the first attempt at determining lightning energy distribution from fulgurites and is also the first data set to measure lightning's energy delivery and its potential damage to a solid earth surface."

The amount of energy in lightning bolts is measured in megajoules (MJ/m). One Mj/m is equivalent to the kinetic energy when a car travels down a highway at 60 miles per hour, Pasek said.

Based on their geological data, Pasek and Hurst calculated that the energy produced by a lightning strike peaked at greater than 20MJ/m.

According to Pasek, a the high voltage in a bolt of lightning can heat the air temperature around a strike to more than 53,000 degrees Fahrenheit. For perspective, that's about five times the temperature of the sun's surface.

When lightning strikes sand, soil, rock or clay, the current flows through the target and heats the material to above its vaporizing level. Rapid cooling then produces the fulgurite.